• Before the industrial era began around 1780, carbon dioxide concentrations measured approximately 270–290 ppm. Concentrations have risen steadily since then, reaching 387 ppm in 2009—a 38 percent increase. Almost all of this increase is due to human activities.

• Since 1905, the concentration of methane in the atmosphere has roughly doubled. It is very likely that this increase is predominantly due to agriculture and fossil fuel use.

• Historical measurements show that the current global atmospheric concentrations of carbon dioxide and methane are unprecedented over the past 650,000 years, even after accounting for natural fluctuations.